The invention relates to magnetic field measuring devices, and more specifically, to magnetic flux microscopes used to produce microscopic magnetic images of samples.
A number of techniques have been developed to image magnetic fields at length scales of a few .mu.m or relatively smaller. These include decoration techniques, magnetoresistive or Hall probe sensors, magneto-optic thin films, magnetic force microscopy, and electron beam interferometry. These have provided limited success and are not practical for high resolution and high sensitivity imaging of fields and flux lines.
Examples of the above techniques are disclosed in the following articles:
"On Inhomogeneities in the Magnetization of Ferromagnetic Materials," Phys. Rev. vol. 38, pp 1903-1905, November 1931 authored by F. Bitter.
"The Structure of the Superconductors in the Intermediate State," J. Phys., vol. 9, pp. 202-210, June 1945 authored by A. Shalnikov.
"Scanning Hall Probe Microscopy of a Vortex Field Fluctuations in La.sub.1.85 Sr.sub.0.15 CuO.sub.4 " authored by A. M. Chang et al., submitted to Phys. Rev. Lett.
"Observation of Magnetic Domains by the Kerr effect," Phys. Rev., vol. 82, pp. 119-120, April 1951 authored by H. J Williams et al.
"Force Microscopy with 1000 A Resolution." Appl. Phys. Lett., vol. 50, pp. 1455-1457, May 1987 authored by Y. Martin et al.
"Magnetic Field Observation of a Single Flux Quantum by Electron-Holographic Interferometry," Phys. Rev. Lett., vol. 62, pp. 2519-2522, May 1989, authored by T. Matsuda et al.
Additionally, a number of susceptometers and magnetometers have been proposed using Superconducting Quantum Interference Devices or SQUIDs. Though previous SQUID systems have been developed to provide high magnetic field resolution they are impractical to implement in an imaging microscope device. The prior art magnetic imaging devices using SQUIDs have relied on the scale of a mm or larger. See for example:
Advances in Biomagnetism, Plenum, New York.: S. J. Williamson, 1989, pp.677-679, authored by D. S. Buchanan et al.
"Gas Floating Technique for Detection of Trapped Flux Quanta." Physics B, vol. 165, pp. 87-88, August 1990 authored by Q. Geng et al.
"A Single-Chip SQUID Magnetometer," IEEE Transactions on Electron Dev., vol 35, No. 12, Dec. 1988 authored by N. Fujimaki et al.
This scale does not provide the resolution required for problems in the manufacturing, microelectronic and magnetic media industries. Moreover, many of the prior art devices and methods are cost intensive to manufacture and implement. Examples of these include various embodiments as shown in U.S. Pat. Nos. 4,801,882 (Daalmans); 4,771,239 (Hoenig); 4,613,817 (Hoenig); 4,591,787 (Hoenig); 4,588,947 (Ketchen); 4,492,923 (Bryam) and 4,613,816 (Zeamer).
In recent years, since the advent of the high transition temperature (T.sub.c) superconductors and related advances in superconductor technology, many industries have found a greater need to measure superconductor characteristics of materials. The process of magnetic imaging at high resolution and high sensitivity of fields in materials has been impractical while low sensitivity measurements have been lengthy or expensive. This has slowed the hopeful discovery of room temperature superconductors and new high temperature superconductors.
In the field of semiconductor/microelectronics testing, there is a need to measure the current flow and image the data relating the operation of semiconductor/microelectronic devices and the related current paths. The devices currently used have proved to be of limited use in these endeavors because they cannot image the flow of small currents in microelectronic structures. These semiconductor testing devices have utilized both non-destructive testing and destructive testing.
With the advent of magnetic resonance imaging in the field of biology, many new discoveries have been made regarding biological and biochemical subjects. Unfortunately, none of the current technologies applied in this field can provide a very sensitive reading in the picotesla range. A high resolution and highly sensitive magnetic flux microscope using SQUID technology is needed in many fields of biology, ceramics, metallurgy, magnetic media, physics, microelectronics and many other fields.